This disclosure generally relates to electrical contact assemblies and methods for making these; more particularly, this disclosure relates to methods for making electrical contact assemblies for devices such as electrical switches, circuit breakers, contactors, and relays.
Contacts and contact assemblies are well known in the art of circuit breakers. Contact assemblies having electrical contacts for making and breaking an electrical current are not only employed in electrical circuit breakers, but also in other electrical devices, such as rotary double break circuit breakers, contactors, relays, switches, and disconnects. The applications for these electrical devices include, but are not limited to, the utility, industrial, commercial, residential, and automotive industries.
The primary function of a contact assembly is to provide a carrier for an electrical contact that is capable of being actuated to separate the contact from a second contact, thereby enabling the making and breaking of an electrical current in an electric circuit. Electrical contacts suitable for the noted applications often include silver, to carry the bulk of the electrical current, and in many cases a refractory material, such as tungsten, nickel, molybdenum, or tungsten carbide, to provide resistance to erosion and impact wear, or graphite to provide resistance to welding of contacts while maintaining low electrical resistance.
The contact is generally bonded to a substrate, such as a contact arm, which is typically, but not necessarily, copper or a copper alloy, in such a manner that the assembly tolerates the thermal, electrical and mechanical stresses experienced during operation of the host device. Failure of contacts often occurs at least in part due to wear from impact and erosion from electrical arcing. Factors that normally contribute to contact degradation include configuration or geometry of contact (different layer/thickness), materials choice, and processing (brazing/welding) defects that may create voids at the interface between the contact and its substrate, which degrades heat transfer from contact to substrate and, independently or additionally, can lead to separation of the contact from the substrate. Hence there is a need for improved fabrication of contact assemblies having suitable wear and erosion resistance and a high-quality interface joining the substrate and the contact.